Llanishen Reservoir

Llanishen Reservoir
Llanishen reservoir (semi-drained)
Location	Llanishen, Cardiff, Wales
Coordinates	51°31′43″N 3°10′21″W / 51.52861°N 3.17250°W / 51.52861; -3.17250Coordinates: 51°31′43″N 3°10′21″W / 51.52861°N 3.17250°W / 51.52861; -3.17250
Type	Reservoir
Primary inflows	Rainfall
Primary outflows	Drainage
Basin countries	United Kingdom
Built	1886
First flooded	1886
Surface area	23.8 ha (59 acres)
Max. depth	9 m (30 ft)
Water volume	1,440,909 m3 (50,885,200 cu ft)
Surface elevation	45 m (148 ft)
Frozen	Last frozen during Winter 09/10

Llanishen Reservoir (Welsh: Cronfa Ddŵr Llanisien) is a Victorian reservoir in North Cardiff in Wales. The reservoir is one of the reservoirs constructed as part of the Taff Fawr scheme for supplying water to Cardiff and was completed in 1886. It forms part of the Nant Fawr Corridor from the top of Roath Park to the countryside beyond Cyncoed.

The reservoir was used for water supply until the mid-1970s when it became redundant. It was then used for leisure activities and for 'topping up' the adjacent Lisvane Reservoir until it was drained completely. After buying Hyder plc, its new owner Western Power Distribution (WPD), proposed to redevelop the reservoir site, but after a series of objections from national governing bodies, the County Council, local residents and both local and national politicians this was blocked. On 30 August 2013 WPD sold both Llanishen and Lisvane reservoirs to CELSA Group.

In January 2016, Welsh Water acquired both Llanishen and Lisvane reservoirs from CELSA Group on a 999-year lease, which allows Welsh Water to use both reservoirs for water supply and recreational purposes while also allowing CELSA UK to continue to take its water supply from the Lisvane reservoir.

In 1881, a report was commissioned on water resources within a reasonable distance of Cardiff. The report concluded that the Taff Fawr scheme would fulfil the town's requirements at the least cost and it was decided to create Llanishen Reservoir. Construction of the reservoir started in 1882 by the engineer James Simpson for the Cardiff Waterworks Company and was completed in 1886.

The reservoir is retained by an earth-filled embankment with a clay core some 10 metres (33 ft) high and about 1,173 metres (3,848 ft) long. The external embankment face is grassed whilst the internal face has stone pitching over the upper part and concrete over the lower part. It has a maximum surface area of water of 23.8 hectares (59 acres) and a capacity of 1,440,909 cubic metres (50,885,200 cu ft).